1. Field of the Invention
The present invention relates to a switching circuit, a control apparatus and a power generation system, and more particularly, it relates to a switching circuit employed for a power generation system including a plurality of power generation modules generating power with renewable energy and a storage portion, a control apparatus, and a power generation system including a switching portion.
2. Description of the Background Art
A power generation system including photovoltaic power generation modules generating power with solar energy which is renewable energy and a storage portion capable of storing the power generated by the photovoltaic power generation modules is known in general. In such a power generation system, it is demanded to efficiently use the power generated in the photovoltaic power generation modules.
A structure raising efficiency for charging power generated in photovoltaic power generation modules into a storage cell is known in general. Such a power generation system is disclosed in Japanese Patent Laying-Open No. 2009-153306, for example.
In the power generation system of the aforementioned Japanese Patent Laying-Open No. 2009-153306, a plurality of photovoltaic power generation modules are regularly connected to a storage portion. Further, the power generation system of the aforementioned Japanese Patent Laying-Open No. 2009-153306 is formed to be capable of switching a connection state between the plurality of photovoltaic power generation modules to a series connection state where the plurality of photovoltaic power generation modules are connected in series with each other and to a parallel connection state where the plurality of photovoltaic power generation modules are connected in parallel with each other. In the aforementioned Japanese Patent Laying-Open No. 2009-153306, output voltage larger than reference voltage of the storage portion is obtained by switching the connection state from the parallel connection state to the series connection state in a case where output voltage of each photovoltaic power generation module is smaller than the reference voltage of the storage portion, whereby it is possible to efficiently perform charging on the storage portion.
Further, a switching circuit capable of switching a connection state (parallel connection, series connection, combined connection of parallel connection and series connection, separation of a specific solar cell or the like) between a plurality of solar cells by connecting the plurality of solar cells with each other through a changeover switch is known in general. Such a switching circuit is disclosed in Japanese Patent Laying-Open No. 11-103537, for example.
In the aforementioned Japanese Patent Laying-Open No. 11-103537, it is possible to output voltage responsive to a load by switching the connection state between the plurality of solar cells in response to the load. In the aforementioned Japanese Patent Laying-Open No. 11-103537, further, it is described that the voltage may be output to the load through a storage apparatus.
In the aforementioned Japanese Patent Laying-Open No. 2009-153306 and the aforementioned Japanese Patent Laying-Open No. 11-103537, however, the capacity of the storage cells (storage apparatus) is not taken into consideration. In a case where the storage cells are fully charged, therefore, the power generated in the photovoltaic power generation modules cannot be stored. In this case, it follows that the unstorable power is discarded, and hence there is such a problem that the power generated in the plurality of photovoltaic power generation modules cannot be efficiently practically used.
While a method of efficiently practically using power generated in photovoltaic power generation modules by making the same reversely flow into a power grid in a case where surplus power is generated is known in general, there are a large number of restrictions in a case of constructing a system obtained by combining photovoltaic power generation modules and storage cells with each other, and it is difficult to efficiently utilize power generated by the photovoltaic power generation modules. While the photovoltaic power generation modules and the power grid are connected with each other through an inverter in a case of adopting a system performing a reverse power flow, for example, driving of the inverter must be stopped when electric service to the power grid is interrupted, and hence the power generated in the photovoltaic power generation modules cannot be utilized.
The present invention has been proposed in order to solve the aforementioned problems, and an object of the present invention is to provide a switching circuit capable of efficiently practically using power generated in a plurality of photovoltaic power generation modules, a control apparatus and a power generation system.